The present invention relates generally to a method and system for identifying and analyzing subterranean objects. More particularly, the invention relates to a method and system for identifying and analyzing subterranean objects with a combination of radar and imaging techniques.
Various methods are known for detecting the presence of subterranean metallic objects. These known methods typically rely on an analysis of how an electromagnetic field is distorted by the presence of the object and may be broadly classified as frequency-domain and time-domain methods. One simple frequency-domain method uses transmission of a substantially sinusoidal signal with fixed frequency. The received signal is synchronously demodulated and passed through a low-pass filter to remove both noise and carrier-related signals. The phase of the demodulated received signal is synchronized with the phase of the transmitted signal. The presence of a conductive object produces a spatial discontinuity in the electromagnetic properties of the target volume, which produce sudden phase changes in the received signal.
A variation of this technique uses multiple-frequency detectors, in which at least two substantially sinusoidal signals are transmitted. An apparatus is configured to select linear combinations of reactive and resistive signals of at least two transmitted signals such that the mildly conductive ground components are substantially canceled, and/or the ironstone resultant ground vector is substantially canceled, while maintaining sensitivity to signals from target conductive objects.
An example of a time-domain method, in which the relevant signals are described in terms of their temporal evolution is pulse-induction metal detection. Such methods send a short pulse of high current into a search coil and produce a magnetic field. Thus, a transient magnetic pulse is used instead of a sinusoidally varying magnetic signal. As the current is terminated, the collapsing magnetic field generates a reflected pulse opposite in polarity and many times greater in amplitude than the original current pulse. This reflected pulse generates electric current in proximate conductive objects, which increase the decay time of the reflected pulse. The resulting change in slope of the reflected pulse""s decay portion is converted to a DC potential proportional to the change in the duration of the reflected pulse. Some pulse-induction detectors employ a binary transmit-receive cycle in which the voltage applied to the transmission coil is equal for every transmission period and zero between transmission periods.
Such technology is adequate for detecting the presence of subterranean metallic objects, but is generally inefficient for covering large areas of land and is largely unable to discriminate between objects that meet defined criteria of interest and those that do not. For example, in the particular application where it is desired to detect unexploded ordnance, it is necessary to discriminate between live ordnance and metallic clutter. This is a particular problem since many unexploded-ordnance remediation sites are decommissioned firing ranges on military bases where there is significant debris from fragments of shattered projectiles. Furthermore, in applications such as the evaluation of subterranean pipelines, it is desirable not only to identify the location of a pipeline, but also to identify defects that may exist in the pipeline requiring repair before an actual rupture.
There is accordingly room for improving diagnostic identifications of subterranean objects and for introducing automation into the process. In addition, the cost for performing such diagnostic evaluations can be reduced significantly by such a system.
Embodiments of the invention thus provide a method and system for analyzing a subterranean volume. A radar source is configured on an airborne vehicle, such as a helicopter. An arrangement of at least one computer system is provided in communication with the radar source and configured to accept instructions from an operator and to operate the radar source. As the vehicle moves in the vicinity of the subterranean volume along a navigation path, a radar signal is propagated with the radar source into the subterranean volume. A reflected radar signal from a subterranean object within the subterranean volume is received. Physical characteristics of the subterranean object are ascertained from the reflected radar signal.
In one embodiment a laser mapping subsystem is also provided on the vehicle in communication with the computer arrangement. The laser mapping subsystem is used to map a ground surface of the subterranean volume.
In another embodiment, a global positioning system is provided on the vehicle in communication with the computer arrangement. The global positioning system is used to ascertain longitude and latitude positions for the subterranean object.
In a further embodiment, an inertial measurement unit is provided on the vehicle in communication with the computer arrangement. The inertial measurement unit is used to determine the actual motion of the vehicle and to compensate for that motion in analyzing the reflected radar signal to ascertain physical characteristics of the subterranean object.
In still a further embodiment, an infrared detector is provided on the vehicle in communication with the computer arrangement. The infrared detector is used to image the ground surface of the subterranean volume. Infrared radiation is detected from the ground surface and correlated with the reflected radar signal. The wavelength of the detected infrared radiation may be in a range between 3 and 5 xcexcm or may be in a range between 8 and 12 xcexcm.
In yet another embodiment, a visible-wavelength electromagnetic radiation detector, such as a charge-coupled device, is provided on the vehicle in communication with the computer arrangement to image the ground surface of the subterranean volume. Visible-wavelength electromagnetic radiation from the ground surface is detected. A signal is digitized from the detected visible-wavelength electromagnetic radiation. The digitized signal is correlated with the reflected radar signal.
In another embodiment, a magnetometer is provided on the vehicle in communication with the computer arrangement. The magnetometer is used to detect the subterranean object independently of the radar signal to decrease the level of false positives.
In an additional embodiment, a hydrocarbon leak detector is provided on the vehicle in communication with the computer arrangement. The hydrocarbon leak detector is used to detect hydrocarbon emission from the subterranean object, particularly in instances where the subterranean object is an underground pipeline that may have defects.
Identification of the subterranean object may be performed by the computer arrangement with a trained evaluation system, such as a neural net or an expert system. Evaluating whether the subterranean object contains a structural anomaly may be performed by comparing the ascertained physical characteristics with expected characteristics. The subterranean object may be a portion of a pipeline or may be unexploded ordnance in different embodiments.